This invention relates generally to equipment used in producing fluid from a well and more particularly concerns tools to enhance the operation of downhole reciprocating pumps.
In downhole reciprocating pump applications, it is generally recommended that the pump plunger stroke not permit the plunger to strike or bump the pump at the bottom of its stroke. Bumping is undesirable because, if the plunger does make contact with the pump, the impact is transmitted to the pump, to the sucker rod string components and to the gear box at the surface, increasing the possibility of damage to all of these components.
However, if bumping is avoided, the plunger often becomes stuck due to clogging, obstructions or debris within the pump. This can result in reduced efficiency in the pumping process and even in down time to clear the clogging, obstruction or debris. It also can cause damage to the pump components.
In order to achieve continuous and efficient pumping while minimizing the risk of damage to the pumping system components, "tapping" has become a very common practice in the industry. "Tapping" is the coordination of the length of the plunger with the available stroke length in the pump so that, at its maximum downstroke, the plunger "taps" rather than "bumps" the pump to release the plunger. While this practice reduces the impact on the pump, it also is not recommended. It is very difficult to establish a suitable "tapping" stroke. When the pump is idle for a period of time, the gas contained in the fluid column has time to release. Therefore, the fluid column is heavier than during normal operation. Consequently, the sucker rod string stretches. Generally, several stroke adjustments are required in order to achieve a suitable "tapping" stroke. Even then, the desired end result is still the impact of the plunger with the pump and the possibility of damage, though reduced, is still great.
In a different approach to the problem, U.S. Pat. No. 5,236,038 issued to Steve Clemshier on Aug. 17, 1993, teaches a pump shaker which is connected in the rod string near the downhole pump. The shaker shakes the pump on every stroke of the rod string in order to free a stuck plunger. However, the shaker permits no relative rotational motion of its components and the plunger, which is connected to the shaker, cannot rotate in relation to the rod string. Thus, the full vertical force applied by the shaker on every stroke is unidirectionally exerted on the plunger and maximum stretching and compression of the plunger occurs on every stroke.
It is, therefore, an object of this invention to provide a tool which eliminates the need for "tapping" in the operation of a downhole pump. Another object of this invention is to provide a tool which reduces the unidirectional application of force to the plunger of a downhole pump. A further object of this invention is to provide a tool that allows the plunger of a downhole pump to take the path of least resistance to overcome a stuck condition.